Add proc for minting test capabilities

src/syndicate/capabilities.nim

@@ -15,6 +15,11 @@ proc mint*[T](key: openarray[byte]; oid: T): SturdyRef =
   let oidPr = toPreserve(oid, Ref)
   SturdyRef(oid: oidPr, sig: hmacSha256(key, encode(oidPr), key.len))
 
+proc mint*(): SturdyRef {.deprecated.} =
+  ## Mint a test capability for the use with the Syndicate server.
+  var key: array[16, byte]
+  mint(key, "syndicate")
+
 proc attenuate*(r: SturdyRef; caveats: Attenuation): SturdyRef =
   result = SturdyRef(
     oid: r.oid,